In the field of graphic arts and medical treatment, there have been concerns in processing of photographic film with respect to effluent produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. There has been desired a photothermographic dry imaging material for photographic use, capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter.
Known as such a technique are silver salt photothermographic dry imaging materials forming photographic images through thermal processing, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075 and Morgan “Dry Silver Photographic Materials” (Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991).
These photothermographic materials are comprised of a light-sensitive layer containing a light-sensitive silver halide and an organic silver salt which function as a photosensor and silver source, respectively and which are thermally developed at a temperature of 80 to 250° C. with the reducing agent to form images, without being further subjected to fixing. Accordingly, to achieve smooth supply of silver ions to silver halide and to prevent deterioration in transparency caused by light scattering, much effort has been put into improvements in the shape of organic silver salt grains which are capable of being suitably arranged in the light-sensitive layer and little adversely affected with light scattering.
However, to achieve the foregoing objects, an attempt to obtain fine grains by means of dispersion and/or pulverization with high energy using a dispersing machine often causes deterioration in silver halide grains or organic silver salt grains, resulting in problems such that fogging is increased and sensitivity is reduced, leading to deteriorated image quality. Therefore, there has been studied a technique of achieving enhanced sensitivity and a high image density without increasing the silver coverage and minimized fogging, as described in JP-A Nos. 2000-53682, 2000-122219, 2001-264921 and 2001-350237 (hereinafter, the term, JP-A refers to an examined Japanese Patent Application Publication).